System for displaying images and method for fabricating the same

ABSTRACT

An exemplary embodiment of a system comprises an active matrix organic electroluminescent device, having a substrate, and a plurality of scan lines and data lines disposed on the substrate, for defining a plurality of pixel regions. Each pixel structure comprises: a switching thin film transistor, a driving thin film transistor, and a storage capacitor. The switching TFT has a light-shielding layer adapted for preventing the sunlight from being incident into the switching TFT. The driving TFT is a bottom gate thin film transistor and have advantages of precisely controlling the current provided to the organic electroluminescent diode. Further, since the storage capacitor has a multilayer structure and occupies a reduced pixel area, the aperture ratio of the pixel structure can be increased.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Division of U.S. patent application Ser. No.11/537,121, filed Sep. 29, 2006 and entitled “System for DisplayingImages and Method for Fabricating the Same,” which is scheduled to issueas U.S. Pat. No. 7,507,998, on Mar. 24, 2009, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a system for displaying images and methods offabricating the same and, more particularly, to a system for displayingimages including active matrix organic electroluminescent devices andmethods of fabricating the same.

2. Description of the Related Art

Please referring to FIG. 1, it is a schematic drawing showing aconventional pixel structure of an active matrix organicelectroluminescent device (AM-OLED). The pixel structure 100 of anAM-OLED is electrically connected to a scan line 102 and a data line104. The pixel structure 100 of the AM-OLED comprises a switching thinfilm transistor 110, a driving thin film transistor 120, a storagecapacitor 130 and an organic light emitting diode 140. The gray level ofthe pixel structure 100 is determined by a data signal input from thedata-line 104. When the switching thin film transistor 110 is turned onby a scanning signal input from the scan line 102, the capacitor 130 ischarged to store the data signal. When the switching thin filmtransistor 110 is turned off, the driving thin film transistor 120 iscontrolled by the data signal stored in the capacitor 130 and a drivingcurrent corresponding to the data signal (gray level) is provided to thelight emitting diode 140 through the driving thin film transistor 120.Specifically, the driving thin film transistor 120 is electricallyconnected to a power source Vdd. The current from the power source Vddis adjusted by the driving thin film transistor 120 and the adjustedcurrent (driving current) is provided to the light emitting diode 140frame by frame.

Please continue to refer to FIG. 1, the switching thin film transistor110 and the driving thin film transistor 120 can be, for example, anamorphous-silicon thin film transistor or a poly-silicon thin filmtransistor. Compared with the amorphous-silicon thin film transistor,the poly-silicon thin film transistor has the advantages of low powerconsumption and high electron mobility. Although the option of thesubstrate is constrained by the temperature for fabricating thepoly-silicon thin film transistor earlier, the poly-silicon thin filmtransistor has become the mainstream of the active device according tothe development of the low temperature poly-silicon technology.

The top gate thin film transistor has the advantages of large processwindow, simple fabrication process and small size. Therefore, top gatethin film transistors are broadly used in the pixel structures and theperipheral circuit of the conventional active matrix organicelectroluminescent devices. The characteristic of top gate thin filmtransistors, however, are sensitive to the cleaning process before dateinsulator deposition, resulting in undesirable clean mura defects in theactive matrix OLED devices.

Besides, for the bottom emission AM-OLED device, when the top gate thinfilm transistors serving as the switching thin film transistor expose tosunlight, current leakage occurs in the channel region even if theswitching thin film transistor is turned off. The data signal stored inthe storage capacitor would deteriorate and therefore affect thestability of the OLED display. Furthermore, the storage capacitor andthe power line occupy the pixel area and this would reduce the apertureratio of the pixel structure.

Therefore, it is necessary to develop a novel active matrix organicelectroluminescent device to solve the aforementioned problems.

BRIEF SUMMARY OF THE INVENTION

Systems for displaying images are provided. An exemplary embodiment of asystem comprises an active matrix organic electroluminescent device,having a substrate, and a plurality of scan lines and data linesdisposed on the substrate, for defining a plurality of pixel regions. Inparticular, each pixel structure comprises a switching thin filmtransistor, a driving thin film transistor, and a storage capacitor. Theswitching thin film transistor comprises a first channel layer, firstsource/drain regions disposed at both sides of the first channel layer,a first gate electrode disposed above the first channel layer, and afirst conductive layer disposed under the channel layer. The drivingthin film transistor comprises a second channel layer, secondsource/drain regions disposed at both sides of the first channel layer,a second gate electrode disposed under the second channel layer, and asecond conductive layer disposed above the second channel layer. Thestorage capacitor comprises two first electrodes, and a second electrodedisposed between the first electrodes, wherein the first conductivelayer, the second gate electrode and the lower first electrode are ofthe same material and formed by the same process. Further, a pixelelectrode electrically connects to the second source/drain regions ofthe driving thin film transistor via a first contact. Wherein, thesecond electrode electrically connects to the second source/drainregions of the driving thin film transistor via a second contact, andthe two first electrodes electrically connect to the first source/drainregions of switching thin film transistor via a third contact.

Methods for fabricating systems for displaying images are also provided.In an exemplary embodiment of a method for fabricating systems fordisplaying images having an active matrix organic electroluminescentdevice, a substrate is provided, wherein the substrate has a switchingthin film transistor region, a driving thin film transistor region, anda storage capacitor region. A first conductive layer, a first gateelectrode, and a lower first electrode are formed respectively withinthe switching thin film transistor region, the driving thin filmtransistor region, and the storage capacitor region. A first dielectriclayer is formed on the substrate to cover the first conductive layer,the lower first electrode, and the first gate electrode. A first polyisland, a second poly island, and a third poly island are formed on thefirst dielectric layer respectively within the switching thin filmtransistor region, the driving thin film transistor region, and thestorage capacitor region. A doping process is subjected to the thirdpoly island to form a second electrode. A second dielectric layer isformed on the substrate to cover the poly islands and the secondelectrode. A second gate electrode is formed on the second dielectriclayer over the first poly island. A higher first electrode is formed onthe second dielectric layer over a part of the second electrode. Asecond conductive layer is formed on the second dielectric layer overthe second poly island. A first source and drain region are formed inthe first poly island to define a first channel region located betweenthe first source and drain regions. A second source region and a seconddrain region are formed in the second poly island to define a secondchannel region located between the second source and drain regions. Apassivation layer is formed on the substrate. A first contact is formedto contact the second drain electrode, and a pixel electrode is formedto electrically connect to the second drain electrode via the firstcontact. A second contact is formed to electrically connect the secondsource electrode and the second source electrode. A third contact isformed to electrically connect the first drain region, the lower firstelectrode, and the high first electrode.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a schematic drawing showing a conventional pixel structure ofan AM-OLED device.

FIG. 2 is a top view illustrating the pixel structure of an activematrix organic electroluminescent device in a system for displayingimages according to an embodiment of the invention.

FIGS. 3 a to 3 q are sectional diagrams of FIG. 2 along line A-A′showing the method for fabricating electroluminescent devices.

FIG. 4 schematically shows another embodiment of a system for displayingimages.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 2 is a schematic top view of one pixel of an embodiment of anactive matrix organic electroluminescent device according to the presentinvention. The active matrix organic electroluminescent device comprisesa plurality of pixel areas 200 arranged in a matrix form. Each pixelarea 200 comprises a switching thin film transistor 210 electricallyconnected to a scan line 201 extending along a X direction, a storagecapacitor 230, an organic electroluminescent diode 240, and a drivingthin film transistor 220 electrically connecting to the organicelectroluminescent diode 240 and a data line 203 extending along a Ydirection. In the present invention, the switching thin film transistor210 comprises a first conductive layer, serving as a floating gate,disposed under a first channel layer and opposite to the gate electrodeof the switching thin film transistor 210. The first conductive layerserving as the light-shielding layer is adapted for preventing thesunlight from being incident into the switching thin film transistor210, so as to improve the current leakage occurred in the channel layer.Particularly, the driving thin film transistor 220 employing in theinvention can be a bottom gate thin film transistor and have advantagesof precisely controlling the current provided to the organicelectroluminescent diode 240, avoiding the cleaning mura defects.Further, since the storage capacitor has a multilayer structure andoccupies a reduced pixel area, increasing the aperture ratio of thepixel structure. FIGS. 3 a to 3 q are sectional diagrams along line A-A′of FIG. 2 illustrating the manufacturing process of the active matrixorganic electroluminescent device 200 according to a preferredembodiment of the invention.

First, please refer to FIG. 3 a, a substrate 205 having a switching thinfilm transistor region 206, a driving thin film transistor region 208,and a storage capacitor region 207. A first metal layer (not shown) isformed on the substrate 205 and patterned to form a first conductivelayer 209 within the switching thin film transistor region 206, a firstgate electrode 212 within the driving thin film transistor region 208,and a lower first electrode 211 within the storage capacitor region 207.Wherein, the lower first electrode 211 and the first gate electrode 212can connect together, referring to FIG. 3 a.

Next, referring to FIG. 3 b, a first dielectric layer 213 is formed onthe substrate 205 to cover the first conductive layer 209, the lowerfirst electrode 211, and the first gate electrode 212.

After that, referring to FIG. 3 c, a poly silicon layer (not shown) isformed on the first dielectric layer 213 and patterned to form a firstpoly island 214 on the first dielectric layer 213 within the switchingthin film transistor region 206, a second poly island 216 on the firstdielectric layer 213 within the driving thin film transistor region 208,and a third poly island 215 on the first dielectric layer 213 within thestorage capacitor region 207. Next, a first patterned photoresist layer217 is formed on the first dielectric layer 213 to cover the second polyisland 216.

Next, referring to FIG. 3 d, a P-type doping process 218 is performed onthe first poly island 214 and third poly island 215.

Next, referring to FIG. 3 e, second patterned photoresist layers 219 aand 219 b are formed on a part of the first poly island 214 and separateby a specific distance, wherein the first patterned photoresist layerremains covering the second poly island 216. Then, referring to FIG. 3f, a heavily N-type doping process 221 is performed on the first polyisland 214 and third poly island 215 by using the patterned first andsecond photoresist layers 217, 219 a and 219 b as the masks in order toform the first source and drain regions 222 and the second electrode 214respectively. The channel regions 223 are located between the firstsource/drain regions 222.

After the heavily N-type doping process 221 is performed, referring toFIG. 3 g, the first and second patterned photoresist layers 217, 219 a,and 219 b are removed. Next, a second dielectric layer 225 and a secondmetal layer (not shown) are sequentially formed on the first dielectriclayer 213 to cover the first source/drain regions 222, the channelregions 223, the second poly island 216 and the second electrode 224.Next, the second metal layer is then patterned to form a second gateelectrode 226 on the second dielectric layer 225 over the channel of thefirst poly island 214, a higher first electrode 227 on the seconddielectric layer 225 over a part of the second electrode 224 (exposing apart of the top surface of the second electrode 224), and a secondconductive layer 228 on the second dielectric layer 225 over the secondpoly island 216.

It should be noted that the scan lines 201 can be formed by the samepatterning process with the second gate electrode 226, the higher firstelectrode 227, and the second conductive layer 228.

After patterning the second metal layer, referring to FIG. 3 h, a lightdoping process 229 with an N-type dopant is performed on the first andsecond poly islands 214 and 216 by using the second gate electrode 226and second conductive layer 228 as the masks, so as to form lightlydoped drains (LDD) 234 in the first poly island 214. After the lightdoping process 229 is performed, the channel layers 223 of the switchingthin film transistor 210 are located between the lightly doped drains(LDD) 234.

Next, referring to FIG. 3 i, a third patterned photoresist layers 235 aand 235 b are formed on the second dielectric layer 225. The thirdpatterned photoresist layer 235 a covers the switching thin filmtransistor region 206, and the third patterned photoresist layer 235 bformed over the second electrode 224 uncovered by the higher firstelectrode 227.

Next, referring to FIG. 3 j, a heavy P-type doping process 236 isperformed on the second poly islands 216 by using the second conductivelayer 228 as the masks, to form a second drain region 237 and a seconddrain region 238

Referring to FIG. 3 k, after the heavily P-type doping process 236 isperformed, the third patterned photoresist layers 235 a and 235 b areremoved. Thus far, the basic structures of the switching thin filmtransistor 210, the storage capacitor 230, and the driving thin filmtransistor 220 are formed. Next, a third dielectric layer 239 is formedon substrate 205 to cover the switching thin film transistor 210, thestorage capacitor 230, and the driving thin film transistor 220, andthen an optional dielectric layer 241 is blanketly formed on the thirddielectric layer 239.

Next, referring to FIG. 31, a plurality of via holes 242˜248 are formedto pass through the optional dielectric layer 241, the third dielectriclayer 239, the second dielectric layer 225, and (or) the firstdielectric layer 213. Specifically, the first and second via holes 242and 243 expose the first source and drain regions 222, the third viahole 244 the lower first electrode 211, the forth via hole 245 the lowerfirst electrode 211, the fifth via hole 246 the second electrode 224,the sixth via hole 247 the second source region 237, and the seventh viahole 248 the second drain region 238.

Next, referring to FIG. 3 m, a first contact 252 is formed toelectrically connect the second drain region 238 through the seventh viahole 248. A second contact 251 is formed to electrically connect thesecond source region 237 (through the fifth via hole 247) and the secondelectrode 224 (through the sixth via hole 246). A third contact 250 isformed to electrically connect the first source and drain regions 222(through the second via hole 243), the lower first electrode 211(through the third via hole 244), and the higher first electrode 227(through the fourth via hole 245). A forth contact 249 is formed toelectrically connect the first source and drain regions 222 through thefirst via hole 242. Specifically, the first contact 252, the secondcontact 251, the third contact 250, and the fourth contact 249 are ofthe same material and formed by the same process with a data line 203(shown in FIG. 2).

Next, referring to FIG. 3 n, a passivation layer 253 is formed on thesubstrate 205, covering the contacts 249˜252. After forming thepassivation layer 253, the passivation layer 253 is patterned to form aeighth via hole 254 passing therethrough, exposing the first contact252.

Next, referring to FIG. 3 o, a pixel electrode 271 is formed toelectrically connect to the second drain region 238 through the firstcontact 252. Next, referring to FIG. 3 p, a pixel definition layer 280is then formed on the passivation layer 253 to define a predetermineddisplay region 285. Suitable material for the pixel electrode 271 istransparent metal or metal oxide, such as indium tin oxide (ITO), indiumzinc oxide (IZO), aluminum zinc oxide (AZO), or zinc oxide (ZnO).Preferably, the transparent anode electrode 105 is formed by sputtering,electron beam evaporation, thermal evaporation, or chemical vapordeposition.

Finally, referring to FIG. 3 q, electroluminescent layers 272 and acathode electrode 273 are sequentially formed on the predetermineddisplay region 285. Specifically, the pixel electrode 271 (serving as ananode), the electroluminescent layers 272, and the cathode electrode 273comprise a organic electroluminescent diode 240. The electroluminescentlayers 272 may comprise a hole injection layer, a hole transport layer,an emission layer, and an electron transport layer, including organicsemiconductor materials, such as small molecule materials, polymer, ororganometallic complex, formed by thermal vacuum evaporation, spincoating, dip coating, roll-coating, injection-filling, embossing,stamping, physical vapor deposition, or chemical vapor deposition. Thecathode electrode 273 can be capable of injecting electrons into anorganic electroluminescent layer, for example, a low work functionmaterial such as Ca, Ag, Mg, Al, Li, or alloys thereof.

In this embodiment, the second gate electrode 226 is electricallyconnected to the scan line 201 (shown in FIG. 2) in order to make theswitching thin film transistor 210 a top gate thin film transistor,while the first conductive layer 209 serves as the floating gate andlight-shielding layer of the switching thin film transistor 210.Besides, the driving thin film transistor can be a bottom gate thin filmtransistor, while the second conductive layer 228 serves as a floatinggate.

The light-shielding layer (first conductive layer 209) can prevent thesunlight from being incident into the thin film transistor, so as toavoid the current leakage occurred in the channel layer. On thecontrary, if the first conductive layer is electrically connected to thescan line, the switching thin film transistor 210 is a bottom gate thinfilm transistor. In light of the above, the switching thin filmtransistor 210 can be a top gate or a bottom gate thin film transistoraccording to different requirements. Therefore, the flexibility ofapplications of the thin film transistors can be enhanced. Further,since the storage capacitor 230 has a multilayer structure and occupiesa reduced pixel area, increasing the aperture ratio of the pixelstructure.

FIG. 4 schematically shows another embodiment of a system for displayingimages which, in this case, is implemented as a display panel 300 or anelectronic device 500. The described active matrix organicelectroluminescent device can be incorporated into a display panel thatcan be an OLED panel. As shown in FIG. 4, the display panel 300comprises an active matrix organic electroluminescent device, such asthe active matrix organic electroluminescent device 200 shown in FIG. 2.The display panel 300 can form a portion of a variety of electronicdevices (in this case, electronic device 500). Generally, the electronicdevice 500 can comprise the display panel 300 and an input unit 400.Further, the input unit 400 is operatively coupled to the display panel300 and provides input signals (e.g., an image signal) to the displaypanel 400 to generate images. The electronic device 500 can be a mobilephone, digital camera, personal digital assistant (PDA), notebookcomputer, desktop computer, television, car display, or portable DVDplayer, for example.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A method of fabricating a system for displaying images, wherein thesystem comprising an active matrix organic electroluminescent device,the method comprising: providing a substrate having a switching thinfilm transistor region, a driving thin film transistor region, and astorage capacitor region; forming a first conductive layer within theswitching thin film transistor region, a first gate electrode within thedriving thin film transistor region, and a lower first electrode withinthe storage capacitor region; forming a first dielectric layer on thesubstrate to cover the first conductive layer, the lower firstelectrode, and the first gate electrode; forming a first poly island onthe first dielectric layer within the switching thin film transistorregion, a second poly island on the first dielectric layer within thedriving thin film transistor region, and a third poly island on thefirst dielectric layer within the storage capacitor region; performing adoping process to the third poly island to form a second electrode;forming a second dielectric layer on the substrate to cover the polyislands and the second electrode; forming a second gate electrode on thesecond dielectric layer over the first poly island, a higher firstelectrode on the second dielectric layer over a part of the secondelectrode, a second conductive layer on the second dielectric layer overthe second poly island; forming first source and drain regions in thefirst poly island to define a first channel region located between thefirst source and drain regions, and second source and drain regions inthe second poly island to define a second channel region located betweenthe second source and drain regions; forming a passivation layer on thesubstrate; forming a first contact to contact the second drain region;and forming a pixel electrode to electrically connect to the seconddrain region via the first contact; forming a second contact toelectrically connect the second electrode and the second source region;and forming a third contact to electrically connect the first source anddrain regions, the lower first electrode, and the high first electrode.2. The method as claimed in claim 1, wherein the lower first electrodeand the first gate electrode are connected.
 3. The method as claimed inclaim 1, wherein the first conductive layer, the first gate electrodeand the lower first electrode are of the same material and formed by thesame process.
 4. The method as claimed in claim 1, wherein the firstpoly island, the second poly island, and the third poly island are ofthe same material and formed by the same process.
 5. The method asclaimed in claim 1, wherein the second electrode, the first source anddrain regions are formed by the same doping process.
 6. The method asclaimed in claim 1, wherein the second gate electrode, the higher firstelectrode, and the second conductive layer are of the same material andformed by the same process with a scan line.
 7. The method as claimed inclaim 1, wherein the first contact, the second contact, and the thirdcontact are of the same material and formed by the same process with adata line.
 8. The method as claimed in claim 1, after forming the firstcontact, further comprising: forming an organic electroluminescent diodeon the passivation layer, wherein the organic electroluminescent diodecomprises the pixel electrode, serving as an anode electrode of theorganic electroluminescent diode, electrically connected to the seconddrain region via the first contact.